The goals of the research proposal include an investigation of the interaction of glutamate and glutamate-like agonists at the glutamate receptor on horizontal cells isolated from the catfish retina. Experments will be carried out to examine the nature of the desensitization that occurs at the glutamate receptor in the presence of high (greater than 100 MuM) concentrations glutamate and the relationship of Mg on the desensitization process. In addition, the glutamate-like analogs kainate and quisqualate will be investigated with regards to this desensitization process. Standard low resistance single electrode voltage clamp methods will be used to record the agonist activated currents in the presence and absence of Mg. It is proposed to examine the changes in filter characteristics of isolated horizontal cells by measuring the impedance of the cell using white noise current injection. These experiments will be done to better characterize the effect of the voltage sensitive conductances on cell impedance properties. In addition, this same method will be used to investigate the changes in electrontonic coupling initiated by dopamine at electrotonic synapses made between horizontal cells. These experiments will be carried out on samll groups (2-5) of isolated but coupled horizontal cells as well as horizontal cells in the intact retina. The role of cAMP in the dopamine initiated uncoupling process will be investigated by using cAMP agonists and antagonists. In conjunction with these experiments, we plan to examine the structure of the electrontonic coupling using the electron microscope.